The present invention relates to an electrically heated melting furnace, particularly a direct current furnace, and preferably to a direct current electric arc furnace provided with a plurality of electrically conductive paths which serve as an electrode and which extend through the refractory material lining of the floor of the furnace.
One generally existing problem in prior art direct current furnaces, is that of insufficient durability of the furnace floor or hearth bottom in the region in which electrically conductive material is disposed to serve as electrodes. Various floor configurations for such direct current furnaces are known in which metal or graphite plates or rods are disposed as current conductors in the furnace lining made of a refractory material. However, these plates or rods are dissolved by the metal melt or may be washed out with it and may then even result in breaks in the furnace.
The graphite component of carbon magnesite blocks or bricks give them a certain electrical conductivity and, for that reason, they have been suggested for use as the conductive material for a floor electrode. However, since the electrical conductivity of such blocks is too low, additional graphite conductors must be used to assure sufficient passage of current. Such additional conduction present the further problem that if these additional conductors contact the metal bath, they are subjected to considerable wear. Moreover, with the high thermal stresses occurring in such a floor, these additional conductors may also be easily crushed, thus interrupting the flow of current at the breaks. Additionally, in certain modes of operating a direct current furnace, it frequently happens that the carbon magnesite blocks wear out very quickly because their graphite components decompose. Finally, the use of carbon magnesite blocks has the additional drawback that their good thermal conductivity causes considerable heat losses during operation of the furnace.